1. Field of the Invention
This invention relates to a lawnmower engine speed control system.
2. Description of the Related Art
Lawnmowers equipped with an engine for powering one or more cutter blades disclosed, for example, in Japanese Laid-open Patent Application No. 2003-111508, are in wide use. In this type of lawnmower, the engine speed is generally controlled to the desired speed by a mechanical governor that mechanically regulates the degree of opening of the throttle valve in response to the engine load.
The mechanical governor operates to maintain the engine speed constant (at the desired speed) utilizing a state of equilibrium between the centrifugal force of revolving fly weights and the force of a spring. With this arrangement, it is impossible to set the desired engine speed during mowing operation (when grass is actually being cut and the engine load is higher than during idling) higher than the desired speed (idling speed) during non-mowing operation (when grass is not being cut and the engine load is low). This means that the desired speed during non-mowing has to be set at least as high as the desired speed during mowing. The lawnmower engine is therefore noisy and low in fuel efficiency during non-mowing operation.
Moreover, in cases where the engine speed is too high during non-mowing operation or too low during mowing operation, the operator has to manually regulate the engine speed. This complicates lawnmower operation and is liable to make stable operation impossible owing to variance of the engine speed.